Wireless communication base station with current limiting capability

ABSTRACT

A wireless communication system base station ( 20 ) includes a base station transceiver ( 26 ) that has at least one operative component ( 32 ) for facilitating wireless communications. A current limiting device ( 36 ) includes at least one field effect transistor for selectively controlling current flow to a capacitive stability device ( 34 ) associated with at least one of the operative components ( 32 ). In the disclosed example, the current limiting device ( 36 ) is in series with the capacitive stability device ( 34 ) but in parallel with the operative component ( 32 ).

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.11/234,900, filed Sep. 26, 2005, which is incorporated by reference asif fully set forth.

FIELD OF INVENTION

This invention generally relates to communication. More particularly,this invention relates to wireless communication systems.

BACKGROUND

Wireless communication systems typically include base stations that arearranged to provide wireless communication service over a selectedgeographic region, for example. Base stations typically include anantenna and a base station transceiver (BTS). The operative componentsof the BTS typically include a DC-DC converter. A stability capacitortypically is placed in parallel with at least the DC-DC converter toprovide stability in a known manner.

Introducing a stability capacitor provides the advantage of morereliable operation, however, there is a drawback. During start-upconditions, for example, the stability capacitor will cause anundesirably high current draw until the capacitor is fully charged, forexample. In some instances, the current rush can be 200 times greaterthan the steady state current of the operative components of the BTS.Such a high current draw may damage some components and, at least,typically triggers a battery or other powering device shutdown.

To address that situation, the typical approach is to include a currentlimiting field effect transistor (FET) that throttles the current to theoperative components during start up conditions. While this approach hasproven useful, those skilled in the art are always striving to makeimprovements. For example, the arrangement of the FET in series with thecapacitive stability device and the operative components requires theFET to be designed to accommodate the steady state current of theoperative components during normal operation. This introduces additionalcost into a BTS. Another issue presented by commonly used currentlimiting FETs is that they require heat sink capability to absorb heatgenerated during operation. Adding additional heat sink components addsfurther cost to a BTS.

It would be useful to have a new arrangement that does not have theadded costs associated with typical current limiting FETs while stillproviding the current protection capability of known arrangements.

SUMMARY

An exemplary embodiment of a base station for use in a wirelesscommunication system includes a power supply. At least one operativecomponent that is powered by the power supply facilities wirelesscommunications. A capacitive stability device is in parallel with the atleast one operative component. A current limiting device is in serieswith the capacitive stability device between the power supply and thecapacitive stability device. The current limiting device is in parallelwith the at least one operative component.

Such an arrangement provides current limiting capabilities withoutrequiring the current for powering the at least one operative componentduring normal operation to flow through the current limiting device. Oneadvantage to this example is that the current limiting device can besized to handle the in rush current to the capacitive stability deviceand then to handle a steady state current flowing toward that device,which is significantly lower than the steady state current flowing tothe at least one operative component. This introduces substantial costsavings in a base station.

An exemplary method of controlling power to at least one operativecomponent within a base station that is useful for facilitating wirelesscommunications includes selectively throttling current to a capacitivestability device that is in parallel with the operative componentwithout throttling the current to the operative component.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates selected portions of a wirelesscommunication system including a base station designed according to anembodiment of this invention.

FIG. 2 schematically illustrates an example arrangement designedaccording to an embodiment of this invention.

FIG. 3 schematically illustrates a selected component of the embodimentof FIG. 2.

FIG. 4 is a graphical illustration showing an example current controlstrategy in one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows selected portions of a wireless communicationsystem including a base station 20. A radio tower 22 supports an antenna24 in a known manner. A base station transceiver (BTS) 26 is used in aknown manner for facilitating communications between the base station 20and at least one mobile station 28.

The BTS 26 includes operative components that facilitate wirelesscommunications in a known manner. One such component is a DC-DCconverter that operates in a known manner. It is desirable to include acapacitive stability device in parallel with the DC-DC converter. Theillustrated example includes such an arrangement.

Referring to FIG. 2, selected portions of the BTS 26 are schematicallyshown. A power supply 30 provides power for the operative components 32to operate as needed to facilitate wireless communications. A capacitivestability device 34 is in parallel with the operative components 32. Inthe illustrated example, the capacitive stability device 34 comprises acapacitor. The capacitor of the capacitive stability device 34 is sizedto meet the needs of a particular situation. Those skilled in the artwho have the benefit of this description will be able to selectappropriate components to meet their particular needs.

The illustrated example includes a current limiting device 36 in serieswith the capacitive stability device 34 to protect against currentoverload conditions such as during start up, for example. In theillustrated example, the current limiting device 36 comprises a fieldeffect transistor (FET). The current limiting device 36 is in serieswith the capacitive stability device 34 and in parallel with theoperative components 32. This is different than traditional arrangementswhere the current limiting device was placed in series with theoperative components 32.

The FET of the current limiting device 36 operates in a generally knownmatter to throttle initial charging current going to the capacitivestability device 34 but presenting very low resistance (e.g., the FET isopen wide) during steady state operation.

The illustrated example includes a gate 38 of the FET coupled with aresistor 40 and a parallel combination of a resistor 42 and a capacitor44. The resistor 40, for example, raises the gate voltage of the FET ina known manner.

Having the current limiting device 36 only in series with the capacitivestability device 34 and in parallel with the operative components 32provides significant advantages.

For example, the FET may be sized for handling the steady state currentflowing to the capacitive stability device 34 rather than the steadystate current flowing to the operative components 32. In one example,the operative components draw a steady state current on the order of 100amps. Some examples include a 90 amp steady state current to theoperative components 32. During steady state operation, the capacitivestability device 34 receives ripple current of a significantly lowermagnitude. Some examples include a 5 amp current during steady stateoperation flowing to the capacitive stability device 34. As known, suchripple currents are associated with switching in a DC-DC converter. TheFET of the current limiting device 36 can therefore be sized toaccommodate a steady state current of approximately 5 amps rather thanone of approximately 100 amps. This allows for cost savings compared toprior arrangements.

Because the FET of the current limiting device 36 can be sized toaccommodate significantly smaller steady state current compared toprevious arrangements, the heat sink capacity in the BTS foraccommodating the FET can be more advantageously and economicallyrealized. The smaller sized FET can be mounted on a circuit boardsubstrate typically used for printed circuit boards. FIG. 3schematically illustrates such a circuit board 50 on which the FET ofthe current limiting device 36 is supported. The circuit board 50provides the primary heat sink capacity for absorbing heat associatedwith operation of the current limiting device 36.

Some examples include a plurality of capacitors within the capacitivestability device 34. One example includes arranging such capacitors inparallel and configuring the current limiting device and the timeconstants to sequentially bring each capacitor on line during start upto control the in rush current in a generally sequential manner. Oneexample includes bringing a first capacitor on line and allowing it tobe nearly completely charged before bringing the next capacitor on line.This results in a lower magnitude for the in rush current over the startup charging time for all of the capacitors combined. One example resultsin a generally saw tooth profile of the charging current over time asshown in the plot 70 of FIG. 4. One example includes FETs in parallelwith each other and in series with respective capacitors. Such astrategy allows for using smaller capacity FETs in a current limitingdevice 36 to realize the advantages of the disclosed example even insituations where there is a relatively large bulk capacitance associatedwith the capacitive stability device 34.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

What is claimed is:
 1. A device for limiting a current through anoperative component powered by a power supply, comprising: a capacitivestability device coupled in parallel with the at least one operativecomponent; and a current limiting device coupled in series with thecapacitive stability device between the power supply and the capacitivestability device, and coupled in parallel with the operative component;wherein the current limiting device is configured to operate in aninitial state to restrain a charging current to the capacitive stabilitydevice, and further configured to operate in a steady state to allow thecharging current to flow to the capacitive stability device.
 2. Thedevice of claim 1, wherein the current limiting device comprises a fieldeffect transistor (FET) connected in series with the capacitivestability device.
 3. The device of claim 2, wherein the current limitingdevice further comprises a set of components connected across theoperative component and to a gate terminal of the FET, for providing abiasing current for the FET.
 4. The device of claim 3, wherein the setof components includes a first resistor connected between a firstterminal of the power supply and a gate terminal of the FET, for raisinga gate voltage of the FET.
 5. The device of claim 3, wherein the set ofcomponents includes a parallel combination of a second resistor and acapacitor connected between the gate terminal of the FET and a secondterminal of the power supply.
 6. The device of claim 1, wherein thecapacitive stability device comprises a capacitor.
 7. The device ofclaim 1, wherein the capacitive stability device comprises a pluralityof capacitors.
 8. The device of claim 7, wherein the current limitingdevice controls power supply to the capacitors in a sequential manner.9. The device of claim 7, wherein the current limiting device comprisesa plurality of FETs in parallel with each other and in series with arespective capacitor of the plurality of capacitors.
 10. The device ofclaim 1, further comprising a circuit board substrate supporting thecurrent limiting device.
 11. The device of claim 10, wherein the circuitboard substrate is a primary heat sink for the current limiting device.12. A method of controlling power supply to an operative component,comprising: providing a current limiting device in series with acapacitive stability device, between the power supply and the capacitivestability device, and in parallel with the operative component;operating the current limiting device in an initial state where thecurrent limiting device restrains a charging current to the capacitivestability device, and without passing a steady state power supply to theoperative component; and operating the current limiting device in asteady state to allow the charging current to flow to the capacitivestability device.
 13. The method of claim 12, wherein the currentlimiting device comprises a field effect transistor (FET) operated topresent a high internal resistance in the initial state and a lowinternal resistance in the steady state.
 14. The method of claim 13,wherein the FET is biased in the initial state and the steady state viaa set of components connected across the operative component and to agate terminal of the FET.
 15. The method of claim 12, wherein, duringthe steady state operation, a ripple current received by the capacitivestability device has a significantly lower magnitude than a currentflowing through the operative component.
 16. The method of claim 12,wherein the capacitive stability device comprises a capacitor.
 17. Themethod of claim 12, wherein the capacitive stability device comprises aplurality of capacitors.
 18. The method of claim 17, further comprisingthe current limiting device controlling power supply to the plurality ofcapacitors in a sequential manner.
 19. The method of claim 17, whereinthe current limiting device comprises a plurality of FETs in parallelwith each other and in series with a respective capacitor of theplurality of capacitors.